Low lead brass alloy and method for producing product comprising the same

ABSTRACT

A low lead brass alloy and a method for producing a product comprising the low lead brass alloy are proposed. The low lead brass comprises 0.05 to 0.3 wt % of lead (Pb); 0.3 to 0.8 wt % of aluminum (Al); 0.01 to 0.4 wt % of bismuth (Bi); 0.1 to 0.15 wt % of microelements; and more than 97.5 wt % of copper (Cu) and zinc (Zn), wherein copper is in an amount ranging from 58 to 70 wt %.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to environmentally-friendly brass alloysand methods for producing products comprising the brass alloys.

2. Description of Related Art

Brasses include copper, zinc and a small amount of impurities, whereincopper and zinc are usually present at a ratio of about 7:3 or 6:4. Itis known that brasses contain lead (mainly ranging from 1 to 3 wt %) toimprove the properties thereof by achieving the desirable mechanicalproperty at the industrial level. Thus, brasses become importantindustrial materials which are widely applicable to products such asmetallic devices or valves used in pipelines, faucets and watersupply/drainage systems.

However, as the awareness of environmental protection increases and theimpacts of heavy metals on human health and environmental pollutionsbecome important public issues, it is a tendency to restrict the usageof lead-containing alloys. Various countries such as Japan, the UnitedStates of America, etc, have sequentially amend relevant regulations,and put intensive efforts to lower lead contents in the environment byparticularly demanding that no molten lead shall leak from thelead-containing alloy materials used in products such as householdelectronic appliances, automobiles and water systems to drinking waterand lead contamination shall be avoided during processing. Thus, thereexists an urgent need in the industry to develop a lead-free brassmaterial, and find an alloy formulation that can substitute forlead-containing brasses while having desirable properties like thecasting property, machinability, corrosion resistance and mechanicalproperties.

Several lead-free copper alloy formulations have been reported. Inexamples where silicon (Si) is added in brass alloys as a majoringredient instead of lead, TW421674, U.S. Pat. No. 7,354,489,US20070062615, US20060078458 and US2004023441 disclose lead-free copperalloy formulations that have poor machinability due to the conventionaltechnologies applied. Further, another lead-free alloy formulation, suchas the one disclosed in CN10144045, contains aluminum, silicon andphosphorus as major alloy elements. Although such alloy formulation canbe used for casting, it has poor machinability as well as significantlylow processing efficiency compared with that of lead-containing brasses.Therefore, the alloy formulation is not suitable for mass productions.Moreover, CN101285138 and CN101285137 disclose lead-free alloyformulations in which phosphorus as a major alloy element, but theapplication of the alloy formulations to casting is prone to causedefects like cracks and slag inclusions.

Alternatively, there are also publications in which bismuth (Bi) isadded in brass alloys as a major component to replace lead. For example,U.S. Pat. No. 7,297,215, U.S. Pat. No. 6,974,509, U.S. Pat. No.6,955,378, U.S. Pat. No. 6,149,739, U.S. Pat. No. 5,942,056, U.S. Pat.No. 5,653,827, U.S. Pat. No. 5,487,867, U.S. Pat. No. 5,330,712,US20060005901, US20040094243, U.S. Pat. No. 5,637,160 and US20070039667disclose that the bismuth contents in the aforesaid alloy formulationscover a range from 0.5 wt % to 7 wt %. In addition to bismuth, each ofthe alloy formulations contains different elemental components andspecific proportions. Further, U.S. Pat. No. 6,413,330 discloses alead-free copper alloy formulation containing bismuth, silicon and othercomponents at the same time, and CN101440444 also discloses a lead-freebrass alloy with high zinc content. However, due to the high siliconcontent and low copper content of alloys, molten alloys have poorfluidity, such that it is difficult to fill in the mold cavity of ametallic mold completely, thereby causing casting defects like misrun.Further, CN101403056 discloses a lead-free brass alloy in which lead isreplaced by bismuth and manganese, but the high bismuth content islikely to cause defects like cracks and slag inclusions, and thecombination of low bismuth content and high manganese content leads tohigh degrees of hardness, resistance to chip breaking, and poormachinability.

Since the sources of bismuth is scarce and the price of bismuth isexpensive, replacement of lead with higher bismuth content productionsof lead-free brasses causes exorbitant product costs which is adverse tocommercialization. Further, problems like poor casting property andineffectiveness to improve material embrittlement are observed in theaforesaid brass alloy formulations.

Further, there are also publications disclosing improved productionprocess of lead-free copper alloys or improved lead stripping processes.For example, U.S. Pat. No. 5,904,783 discloses a method for reducinglead leaching into a fluid supply by treating a brass alloy with sodiumand potassium at a high temperature. TW491897 discloses a productionprocess for a brass alloy containing 1 to 2.6 wt % of bismuth. However,conventional lead stripping processes can only reduce leaching of thelead in contact with water surface during immersion of a lead-containingproduct in water, and therefore the lead content of raw materials cannotbe reduced to less than 0.3 wt %.

SUMMARY OF THE INVENTION

In view of the above, an aspect of the present invention is to develop alow lead brass alloy material and improved process of the same.

In order to attain the above and other aspects, the present inventionprovides an environmentally-friendly low lead brass alloy, comprising0.05 to 0.03 wt % of lead (Pb), 0.3 to 0.8 wt % of aluminum (Al), 0.01to 0.4 wt % of bismuth (Bi), 0.1 to 0.15 wt % of microelements and morethan 97.5 wt % of copper (Cu) and zinc (Zn), wherein copper is in anamount ranging from 58 to 70 wt % of the lead brass alloy.

In one embodiment, the low lead brass alloy of the present inventioncomprises copper and zinc in a total amount ranging from 97.5 to 99.54wt %, and preferably more than 98 wt %. In another embodiment, copper isin an amount ranging from 58 to 70 wt % of the total weight of the lowlead brass alloy. Copper present in the aforesaid amounts can provideexcellent toughness and processability. In a preferred embodiment,copper is in an amount preferably ranging from 62 to 65 wt %.

In the low lead brass alloy of the present invention, lead is in anamount ranging from 0.05 to 0.3 wt %. In a preferred embodiment, lead isin an amount ranging from 0.1 to 0.25 wt %, and preferably ranging from0.15 to 0.25 wt %.

In the low lead brass alloy of the present invention, aluminum is in anamount ranging from 0.3 to 0.8 wt %. In a preferred embodiment, aluminumis in an amount ranging from 0.4 to 0.7 wt %, and preferably in anamount ranging from 0.5 to 0.65 wt %. Addition of adequate amounts ofaluminum can increase the fluidity of a copper liquid, and improve thecasting property of the alloy material.

In the low lead brass alloy of the present invention, bismuth is in anamount less than 4 wt %. In a preferred embodiment, bismuth is in anamount ranging from 0.01 to 0.4 wt %, preferably ranging from 0.05 to0.3 wt %, and more preferably ranging from 0.1 to 0.2 wt %.

The microelements comprised in the low lead brass alloy of the presentinvention in an amount ranging from 0.1 to 0.15 wt % can be rare earthelements and/or unavoidable impurities, wherein the rare earth elementscomprise cerium, scandium, yttrium and lanthanide elements. The rareearth elements can be used alone or in a combination of at least twoelements. Addition of adequate amounts of rare earth elements (such ascerium (Ce)) can significantly refine the as-cast microstructure of analloy material, induce changes in the relative amounts and crystalmorphologies of α and β phases after recrystallization annealing, andform impurity particles with elements such as lead, thereby improvingthe distribution of the impurities in an alloy material as well as thephysical property and processability of an alloy. In one embodiment, therare earth element is cerium, which is in an amount ranging from 0.1 to0.15 wt %.

The low lead brass alloy of the present invention further comprisesphosphorus (P) in an amount less than 0.8 wt %. In a preferredembodiment, phosphorus is in an amount ranging from 0.4 to 0.8 wt %.Addition of adequate amounts of phosphorus can increase fluidity ofmelt, thereby improving the weldability of copper and an alloy.Phosphorus has high solid solubility in copper and CuP has low surfaceenergy, so that the surface tension of copper can be lowered, therebyfacilitating precipitation of bismuth in the form of particles.

In the present invention, Bi is used to replace Pb for maintaining themachinability of brass. Pb phase is face-centered cubic lattices with alattice constant of 4.949×10⁻¹⁰ m, and Pb has extremely low solidsolubility in Cu. Hence, Pb is always present in a Cu alloy in the formof a single phase. Bi phase is rhombohedral lattices with a latticeconstant of 4.7457×10⁻¹⁰ m, and Cu and Bi in solid states are notmutually dissolvable. Therefore, a small amount of Bi can lead to thepresence of a single Bi phase in the structure. Bi is constantlydistributed on a grain boundary of brass in the form of a continuousbrittle thin film, and generates hot shortness as well as coldshortness. Bi is segregated on the grain boundary by two mechanisms, asshown in FIG. 8.

The mechanisms responsible for segregation of Bi on the grain boundarycan be explained by two mathematical models, which are illustrated inFIG. 8 by McLean's Model and Hofmann-Ertewein's Model. FIG. 8A shows amodel where volumes are expanded and the model is based on the rule thatBi atoms diffuse from a bullion into the grain boundary (i.e. Fick'sLaw), and FIG. 8B shows a dislocation pipe diffusion model to illustratethe mechanism and the model is based on the rule that liquid Bi flowsinto a dislocation pipe, which acts as a delivery pipe to transfer theliquid Bi to the grain boundary (i.e. dislocation diffusion mechanism).The diffusion rate of the latter diffusion mechanism is 105 times higherthan that of the former diffusion mechanism. When the precipitation ofBi is based on the dislocation-pipe diffusion model, double phaseregions of Cu solid solution and L (liquid Bi) are formed, and in turnleading to the formation of the so-called thin-filmed Bi, therebysignificantly increasing the material embrittlement. To improve thesituation, a rapid cooling approach is applied when the temperature islowered to below 750° C., causing the dislocation and diffusion of thedouble phase regions to disappear and preventing Bi from segregating onthe gain boundary so as to avoid the material embrittlement.

In the present invention, phosphorus is further added to the brass alloyfor reducing the surface tension thereof. This makes the ratio of thesurface tension of the included angle between heterogeneous phases andthe surface tension of the included angle between homogenous phasesapproximate to 0.5. If a dihedral angle is greater than 60 degrees, Biin the brass alloy formulation will precipitate in the form of Biparticles. The machinability of the alloy material is increased to anextent that it does not generate casting defects therein.

In one embodiment, the low lead brass alloy of the present inventioncomprises 0.05 to 0.3 wt % of lead, 0.3 to 0.8 wt % of aluminum, 0.01 to0.4 wt % of bismuth, 0.1 to 0.15 wt % of microelements (i.e. rare earthelements and/or unavoidable impurities), less than 0.8 wt % ofphosphorus, and 98 to 99.54 wt % of copper and zinc, wherein Cu is in anamount ranging from 58 to 70 wt %.

In another embodiment, the low lead brass alloy of the present inventioncomprises 62 to 65 wt % of copper, 0.05 to 0.25 wt % of lead, 0.5 to0.75 wt % of aluminum, 0.2 to 0.3 wt % of bismuth, less than 0.8 wt % ofphosphorus (and the total amount of aluminum and phosphorus is less than1.4 wt %), 0.1 to 0.15 wt % of cerium and residual zinc, and less than0.1 wt % of unavoidable impurities.

Further, the present invention provides a method for producing a productcomprising a low lead brass alloy, comprising the steps of: (a)preheating the low lead brass alloy and foundry return to a temperatureranging from 400° C. to 500° C.; (b) melting the low lead brass alloyand the foundry return to boiling to form a molten copper liquid; (c)preheating the mold to 200° C. and placing sand core into the mold; (d)casting the molten copper liquid into the mold at a temperature rangingfrom 1010 to 1060° C. to obtain a casting part; and (e) releasing thecasting part from the mold.

The method of the present invention can further comprise a step ofpreparing the sand core by mixing one or more selected from the groupconsisting of rounded sand having particle diameters respectivelyranging from 40 to 70 meshes, 50 to 100 meshes and 70 to 140 meshes witha resin and a curing agent, wherein the resin is a urea formaldehyderesin and/or a furan resin. The sand core used in the method of thepresent invention must be sufficiently dried to lower the number of voiddefects.

In one embodiment, a sand washing treatment is performed prior to step(a), so as to remove sand and iron wires.

In another embodiment, the weights of the lead-free copper bullion andthe foundry return are at a ratio ranging from 6:1 to 9:1, preferablyranging from 6:1 to 8:1, and more preferably 7:1.

Step (b) of the present invention can further comprise the step ofadding refining slag, wherein the refining slag is preheated to atemperature above 400° C. prior to the addition.

In an embodiment, the refining slag is added in an amount ranging from0.1 to 0.5 wt %, preferably ranging from 0.15 to 0.3 wt %, and morepreferably 0.2 wt % based on the total weight of the lead-free copperbullion and the foundry return. In step (b), the refining slag can beadded singly or by separate fractions.

In step (d) of the present invention, the casting of the molten copperliquid can be gravity casting. The casting temperature in step (d) needsto be maintained at a range from 1010° C. to 1060° C. Casting isperformed by batches, wherein the casting amount is about 1 to 2kilograms in every batch, and the casting time is about 3 to 8 seconds.

In the method of the present invention, releasing of the mold isperformed 10 or 15 seconds after the casting or till the casting is notred and hot. In a preferred embodiment, the casting part released fromthe mold is cooled by natural cooling.

The method of the present invention can further comprise the followingsteps after step (e): cooling the mold and maintaining the temperatureof the mold ranging from 180 to 220° C.; and cleaning the mold (forexample, by blowing compressed air onto the surface of the mold) andspreading a small amount of graphite liquid on the surface of the mold(for example, spraying with a sprayer) for the next casting.

In an embodiment, the mold is immersed in and cooled with graphiteliquid for 3 to 8 seconds. The graphite liquid is preferably maintainedat a temperature ranging from 25 to 40° C., and the specific weight ofthe graphite liquid ranges from 1.02 to 1.10.

RIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing the solidified state of a moltenlow lead brass of the present invention;

FIG. 2 shows the morphology of a specimen of a low lead brass of thepresent invention viewed under a scanning electronic microscope (SED)and a quantitative analysis performed on the elements present in amicroscopic region by using an X-ray energy dispersive spectroscope(EDS);

FIG. 3A shows the metallographic structural distribution of the specimenof the low lead brass of the present invention;

FIG. 3B shows the metallographic structural distribution of a specimenof a lead-free bismuth brass;

FIG. 3C shows the metallographic structural distribution of a specimenof a C85710 lead brass;

FIG. 4A shows material cracking in the specimen of a lead-free bismuthbrass;

FIG. 4B is an enlarged view showing cracks in the specimen of alead-free bismuth brass;

FIG. 5A shows the metallographic structural distribution afterperforming a test of dezincification corrosion resistance on thespecimen of a lead-free bismuth brass;

FIG. 5B shows the metallographic structural distribution afterperforming a test of dezincification corrosion resistance on thespecimen of a low lead brass according to the present invention;

FIG. 6A shows the chip breaking from a lead-free bismuth brass;

FIG. 6B shows the chip breaking from a C85710 lead brass;

FIG. 6C shows the chip breaking from a low lead brass of the presentinvention;

FIG. 7 is a schematic diagram showing the production of a productcomprising the low lead brass according to the present invention; and

FIGS. 8A and 8B illustrate mechanisms for segregating bismuth in analloy on a grain boundary.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The detailed description of the present invention is illustrated by thefollowing specific examples. Persons skilled in the art can conceive theother advantages and effects of the present invention based on thedisclosure contained in the specification of the present invention.

Unless otherwise specified, the ingredients comprised in the low leadbrass alloy of the present invention are all based on the total weightof the alloy, and are expressed in weight percentages (i.e. wt %).

The present inventors found that when a high bismuth content (i.e. morethan 1 wt %) is added to the brass alloy conventionally, at the microlevel, thin liquid Bi films are easily formed in the grain of the brassalloy, and later generate continuously flaky bismuth by segregation onthe grain boundary to mask it, so that the mechanical strength of thealloy breaks down and the hot shortness and cold shortness of the alloyin turn increase, thereby causing material cracking. Nevertheless,according to the low lead brass alloy formulation of the presentinvention, only less than 0.4 wt % of bismuth is needed. This can solvematerial cracking, and achieve the required material characteristics(such as machinability) of lead brasses (such as conventional C85710lead brasses) without the likeliness to cause product defects likescracks and slag inclusions. Hence, the amount of bismuth used in the lowlead brass alloy of the present invention can be significantlydecreased. This is effective in lowering the production costs of lowlead brass alloys, and extremely advantageous in commercial-scaleproductions and applications.

Moreover, according to the low lead brass alloy formulation of thepresent invention, the lead content of the alloy can be lowered to arange from 0.05 to 0.3 wt %, to conform to the stipulated internationalrequirement for the leads contents in water pipelines. Hence, the lowlead brass alloy according to the present invention is applicable toapplications to manufacturing of faucets and laboratory components,water pipelines and water supply systems.

In one embodiment, the low lead brass alloy of the present inventioncomprises 0.05 to 0.3 wt % of lead, 0.3 to 0.8 wt % of aluminum, 0.01 to0.4 wt % of bismuth, 0.1 to 0.15 wt % of microelements (i.e., rare earthelements and/or unavoidable impurities) and 97.5 to 99.54 wt % of copperan zinc, wherein copper is in an amount ranging from 58 to 70 wt %.

The present invention is illustrated in details by the exemplaryexamples below. Example 1:

In the example 1, the ingredients (the unit weight percentages) of thelow lead brass alloy of the present invention are as follows:

Cu: 62.51 Zn: 35.72 Pb: 0.177 Bi: 0.154 Al: 0.478 P: 0.52 Sn: 0.183 Ce:0.114.

A scanning electron microscopy (SEM) and an X-ray energy dispersivespectroscope (EDS) are used to analyze the morphology, composition andmechanism of a specimen of the brass. Results are shown in FIGS. 1 and 2and Table 1. As shown in the microscopic image in FIG. 2, spot A is αphase and high in copper content, and has a small amount of bismuth ingrains; spot B is β phase and high in zinc content, and does not containbismuth; and spot C is a grain boundary, and has more bismuthprecipitated therefrom to form soft spots which are prone to chipbreaking, thereby increasing the machinability of the material. Analysesof the compositions of spots A, B and C of the specimens of the lowbismuth brass are shown in FIG. 1.

TABLE 1 Analysis of energy dispersion spectra (atomic percentage) A (α)B (β) C Cu 63.03 51.91 61.09 Zn 24.31 42.87 35.1 Bi 0.09 0 2.37 Pb 0.250.17 0.04 Al 0.67 0.53 0.1 P 8.01 1.76 0.26

Test Example 1

Under the same producing and operating conditions, the low lead brassalloy (examples 2 to 4) of the present invention, lead-free bismuthbrass alloy (comparative examples 1 to 4), H-59 lead brass alloy(comparative examples 5 and 6), and high phosphorus lead brass alloy(comparative example 7) were used as materials to produce the sameproduct. The processing characteristics of each alloy and the yield ofproduction at each stage were compared, wherein the yield is defined asfollows:

yield of production=the number of non-defective products/the totalnumber of products×100%

The yield of production reflects the qualitative stability of theproduction. High qualitative stability ensures normal production.

TABLE 2 Statistical data of the products high the low lead phosphorusbrass of the lead-free bismuth brass C85710 brass lead brass presentinvention comparative comparative comparative comparative comparativecomparative comparative example example example category example 1example 2 example 3 example 4 example 5 example 6 example 7 2 3 4measured Cu 62.48 62.57 63.01 61.96 61.5 61.1 62.29 63.35 61.12 62.51content (%) measured Al 0.513 0.556 0.563 0.555 0.607 0.589 0.537 0.5150.531 0.524 content (%) measured Pb 0.0075 0.0042 0.0067 0.0047 1.471.54 0.117 0.182 0.151 0.143 content (%) measured Bi 0.762 0.549 0.3120.147 0.0119 0.0089 0.125 0.117 0.149 0.116 content (%) measured P0.0024 0.0083 0.0074 0.0041 0.0002 0.0002 0.947 0.435 0.584 0.721content (%) yield in 71% 78% 85% 88% 96% 95% 83% 93% 92% 92% castingyield 84% 82% 81% 77% 99% 99% 97% 98% 99% 97% in mechanical processingyield 89% 88% 90% 91% 92% 94% 94% 96% 95% 95% in casting polishing totalyield 53.1%   56.3%   62.0%   61.7%   87.4%   88.4%   75.7%   87.5%  86.5%   84.8%  

As shown in FIG. 2, when lead-free bismuth brass is used as a materialfor product casting, more casting defects are found in the obtainedcasting part. Thus, the total yield of production is lower than 70%. Thehigher the bismuth content, the lower the yield. The major defectsobserved in the casting part in which lead-free bismuth brass is used asmaterial are voids, slag inclusions, cracks, misrun and shrinkage. Thedefective products with the above defects comprise 72% of the totalnumber of defective products. Specifically, the fluidity of the moltencopper liquid of the lead-free bismuth brass is low and the filling ofthe mold is poor, such that the casting part is prone to misrun.Cracking is likely to occur in the casting part, and some minor cracksare not found until the final polishing step. Slag inclusions and voidsare likely to occur in the casting part. Further, the machinability oflead-free bismuth brass is poor, such that problems like vibration andadhesion are likely to occur, thereby causing low yield duringsubsequent mechanical processing.

Moreover, when the low lead brass of the present invention is used as araw material in the test group, the yield is the best (i.e. higher than90%), and the material fluidity of the low lead brass is close to thatof the conventional C85710 lead brass. After performing optimization ofthe casting art, an equiaxed dendritic crystal phase structure with lowoccurrence of embrittlement is obtained after the casting partsolidifies. While ensuring the machinability, the above structureensures that defects like cracking is not prone to occur, so that theentire material can suffice the production requirements. Among them,high phosphorus content is likely to cause casting defects in brassalloys, and lower yield. Therefore, the phosphorus content of the lowlead brass of the present invention should not be more than 0.8%.Further, the corrosion resistance of the low lead brass of the presentinvention is improved compared with the lead-free high bismuth brass incomparative examples 1 and 2.

Test Example 2

A specimen of a brass material was placed under a metallographicmicroscope to examine the structural distribution of the material. Theresults magnified at 100-fold is shown in FIG. 3.

The measured values of the ingredients of the low lead brass in example1 were Cu: 63.35 wt %, AI: 0.515 wt %, Pb: 0.182 wt %, Bi: 0.117 wt %,P: 0.425 wt %. The structural distribution of the low lead brass isshown in FIG. 3A, wherein an equiaxed dendritic crystal phase structureis shown, and the material is prone to chip breaking and can providegood machinability due to the grains shown as dendritic phases. Further,the crystal phase structure has low occurrence of embrittlement, therebynot being likely to have defects like cracks.

FIG. 3B shows a structural distribution in comparative example 1, themeasured values of the major ingredients of the lead-free bismuth brassare Cu: 62.48 wt %, Al: 0.513 wt %, Pb: 0.0075 wt %, Bi: 0.762 wt % andP: 0.0024 wt %. When bismuth content is high, more heterogeneousnucleation sites are formed and nucleation rates are high; and when thecomposition of a phase is over cooling, the grains formed are mainlydendritic and rarely massive crystals. Hence, bismuth segregates on thegrain boundary and generates continuously flaky bismuth, so that themechanical strength of the material breaks down and the hot shortnessand cold shortness are increased, thereby causing the material to crack.

FIG. 3C shows the structural distribution in comparative example 6,wherein the measured values of the ingredients of the C85710 lead brasswere Cu: 61.1 wt %, Al: 0.589 wt %, Pb: 1.54 wt %, Bi: 0.0089 wt % andP: 0.0002 wt %. a phase of the alloy is round-shaped and has goodtoughness, and thus it is not likely to have defects like cracks.

Among them, the specimen of the lead-free high bismuth brass incomparative example 1 cracked naturally after casting. FIG. 4A showscracks of the specimen, and FIG. 4B shows results of an observation ofthe specimen under a stereo microscope. As shown in FIGS. 4A and 4B,sites with higher bismuth contents were likely to have bigger gaps alongthe direction of the grain boundary, thereby lowering the mechanicalstrength.

Test Example 3

A dezincification test was performed on the brass alloys in examples 3and 4 to examine the corrosion resistance of brass. The dezincificationtest was performed according to the standards set forth in AustralianAS2345-2006 “Anti-dezincification of copper alloys”. Before a corrosionexperiment was performed, a novolak resin was used to make the exposedarea of each brass be 100 mm², the specimens were ground flat using a600# metallographic abrasive paper following by washing using distilledwater, and the specimens were baked dry The test solution was 1% CuCl₂solution prepared before use, and the test temperature was 75±2° C. Thespecimens and the CuCl₂ solution were placed in a temperature-controlledwater bath to react for 24±0.5 hours, and the specimens were removedfrom the water bath and cut along the vertical direction. Thecross-sections of the specimens were polished, and then the depths ofcorrosion thereof were measured and observed under a digitalmetallographic microscope. Results are shown in FIG. 5.

As shown in FIG. 5, the average dezincified depth of the lead-free lowbismuth brass (Bi: 0.147%) in comparative example 4 was 324.08 mm; andas shown in FIG. 5B, the average dezincified depth of the low lead brass(Bi: 0.149%) of the present invention was 125.36 mm. The above resultsproved that low lead brass of the present invention had betterdezincification corrosion resistance.

Test Example 4

A mechanical property test was performed on the brass alloys accordingto the standards set forth in IS06998-1998 “Tensile experiments onmetallic materials at room temperature”. Results are shown in Table 3.

TABLE 3 Results of the mechanical property test mechanical propertytensile strength (Mpa) elongation (%) Type of material 1 2 3 4 5 average1 2 3 4 5 average Comparative 372 358 349 367 375 364.2 15 14 11 12 1012.4 example1 Comparative 356 337 363 374 367 359.6 12 11 13 13 12 12.2example5

As shown in Table 3, the tensile strength and elongation of the low leadbrass alloy of the present invention were comparable to those of theC85710 lead brass. This means that the low lead brass of the presentinvention has the same mechanical property as that of the C85710 leadbrass, indicating that the C85710 lead brass can be replaced by the lowlead brass of the present invention in manufacturing of products.

Test Example 5

A test was performed according to the standards set forth in NSF61-2007a SPAC for the allowable precipitation amounts of metals inproducts, to examine the precipitation amounts of the metals of thebrass alloys in aqueous environments. Results are shown in Table 4.

TABLE 4 Precipitation amounts of metals in the products comparativeexample 5 Upper limit of (after a lead standard value comparativestripping Element (ug/L) example 5 treatment) example 1 lead (Pb) 5.019.173 0.462 0.281 bismuth (Bi) 50.0 0.011 0.006 0.023 aluminum (Al) 5.00.093 0.012 0.146

As shown in FIG. 4, various metal precipitation amounts of the low leadbrass of the present invention were lower than the upper limits of thestandard values, and therefore, the low lead brass of the presentinvention conforms to NSF 61-2007a SPAC. Further, the low lead brass ofthe present invention clearly had a lower precipitation amount of theheavy metal, lead, than that of the C85710 lead brass. Thus, the lowlead brass of the present invention is more environmentally friendly,and more beneficial to human health.

Test Example 6

A machinability test was performed on the low lead brass in example 1,the lead-free bismuth brass in comparative example 1 and the C85710 leadbrass in comparative example 5, respectively, on a lathe. Themachinability test was set at the following conditions: 2 mm of feedamount, 950 rpm of rotating speed, and 0.21 mm/rev of charging amount.Results are shown in FIGS. 5 and 6.

TABLE 5 Results of the machinability test on the brasses in example 1,comparative examples 1 and 5 comparative comparative example 1 example 5example 1 Category 1# 2# 1# 2# 1# 2# machining energy u 979.84 998.32809.93 816.72 839.78 832.43 (N/mm²) machining Ff (N) 178.34 162.49 95.47100.54 118.65 104.82 resistance Fp (N) 42.72 37.23 23.31 21.72 28.6924.62 Fc (N) 349.31 336.89 212.97 231.83 254.26 227.36 machining formschips broke were curvy chips broke were chips broke were andcontinuously needle-shaped and needle-shaped or flaky formeddisintegrated and disintegrated

In the machinability tests, machining resistance of the lead-freebismuth brass was the highest in axial direction (Ff), longitudinaldirection (Fp) and normal direction (Fc), and the machining resistanceof the low lead brass of the present invention was closer to that of theconventional C85710 lead brass. The machining energy was also maximumfor the lead-free bismuth brass, and closer to that of the conventionalC85710 lead brass.

Moreover, as shown in FIG. 6, due to the distribution of lead on thebrass substrate by dispersing soft spots, the chips broke from C85710lead brass were disintegrated and round-shaped or needle-shaped and hadgood machinability (see FIG. 6B); the chips broke from the low leadbrass of the present invention were similar to that of the C85710 leadbrass (see FIG. 6C); and the chips broke from the lead-free bismuthbrass was flaky and had poor machinability (see FIG. 6A).

It can be elucidated from each of the above test examples that themachinability of the lead-free bismuth brass material is poorer thanthat of the conventional C85710 lead brass, and is prone to have cuttingproblems like vibration and adhesion, thereby causing the yield in thesubsequent mechanical processing to be overly low. Thus, lead-freebismuth brass is not a suitable replacement of a lead brass alloy.Further, when the lead-free bismuth brass material is used inmanufacturing of products, slag inclusions, voids and cracks are likelyto occur in casting parts. Cracks are often not found until thepolishing step is reached, and production costs are higher. Hence, thelead-free bismuth brass is not suitable for industrial applications.

The low lead brass alloy of the present invention has a mechanicalproperty (for example, machinability) comparable to that of the C85710lead brass and is better than that (for example, tensile strength andelongation) of the conventional C85710 lead brass, and the yield ofproduction and mechanical processing of the casting parts are also good.Further, the precipitation amount of lead from the low lead brass of thepresent invention is significantly lowered, thus it is an extremelysuitable alloy material to replace conventional lead brasses.

Test Example 7

Brasses, of the present invention, for use in faucets were castenvironmentally friendly as shown in FIG. 7.

The rounded sand having particle diameters ranging from 40 to 70 meshes,50 to 100 meshes and 70 to 140 meshes, an urea formaldehyde, a furanresin and a curing agent were used as raw materials to prepare sand coreusing a core shooter, and the gas evolutions of the resins were measuredusing a testing machine. The obtained sand core must be completely usedwithin 5 hours, or it needs to be baked dry.

The low lead brass alloy of the present invention and the foundry returnwere preheated for 15 minutes to reach a temperature higher than 400°C., and the two were mixed at a weight ratio of 7:1 for melting in aninduction furnace until the brass alloy reached a certain molten state(hereinafter referred to as molten copper liquid). An analysis wasperformed on a copper alloy sample, and an ingredient analysis wasperformed using a direct reading. After verifying that the chemicalcomposition of the copper alloy complies with the requirement, castingwas performed by coupling a metal gravity casting machine with the sandcore and a gravity casting mold. A monitoring system was further usedfor controlling, so as to maintain casting temperature between 1010 and1060° C.

In order to avoid reducing the number of casting defects caused by greattemperature variations during casting, each charging amount waspreferably limited to 1 to 2 kg, and the casting temperature wascontrolled to between 3 to 8 seconds. The surface of the molten copperliquid and the spoon were cleaned after each charging, and the surfaceof the molten copper liquid was observed with an eye to avoid anexcessive amount of impurities floating thereon, and checking the spoonto avoid adhesion of an excessive amount of oxides thereon. If thecasting part is a steel die, a furnace slag cleaning process wasperformed after casting 5 to 8 molds, and if the casting part is acopper die, a furnace slag cleaning process was performed after casting20 molds.

When the casting part from each mold was released, the mold was cleanedusing an air gun to ensure that the site of the core head is clean. Thegraphite liquid was spread on the surface of the mold following bycooling by immersion. The temperature of the graphite liquid for coolingthe mold was preferably maintained between 30 to 36° C. Before each ofthe casting, the concentration of the graphite liquid was measured usinga hydrometer, so as to control the specific weight of the graphiteliquid to between 1.05 and 1.06. The impurities in the water tank mustbe removed, so as to reduce the defects in the appearances of thecasting parts. The graphite liquid was cooled collectively by a centralcooling system, passing through a channel to allocate cooling water toeach of the water tanks of the gravity casting machine, following byimmersing the molds into the water tanks to reach cooling effects.

After the molds were cooled, the molds were opened, the castings werereleased and the casting heads were cleaned. The temperatures of themolds were monitored, so as to control the temperatures to between 200and 220° C. to faun casting parts. Subsequently, the casting parts werereleased. During releasing of molds, the casting parts should be removedand set aside carefully, so as to avoid the casting parts from beingdestroyed in a red and hot state.

After the molten copper liquid in an induction furnace was completelycast, self-inspection was performed on the cooled casting parts and thecasting parts were then cleaned in a sand cleaning drum. Then, anas-cast treatment was performed, wherein a thermal treatment fordistressing annealing during casting of as-casts was performed onas-casts to eliminate the internal stress generated by casting. Theas-casts were subsequently mechanically processed and polished, so thatno sand, metal powder or the other impurities adhered to the cavities ofthe casting parts. The as-casts were completely enclosed, so as toperform sealing tests on shells and spacers in water. Afterwards, theas-casts were classified for stocking after a product inspectionanalysis was performed.

By the process of the present invention and taken the 6Ms (i.e., man,machine, material, method, measurement and mother nature) into fullconsiderations, lead-free brass was produced by gravity casting.Production conditions such as temperature and time were strictlyspecified, so as to effectively control each of the variable factors.Undesirable situations which are usually observable in products wereminimized.

In conclusion, the low lead brass alloy of the present invention canimprove the casting property of the material, and has good toughness andexcellent machinability. These can achieve the required materialcharacteristics of conventional lead brasses while not necessarily leadto production of casting defects. Therefore, the alloy material of thepresent invention is suitable for applications to subsequent processes.Further, the low lead brass alloy material of the present invention isnot likely to generate defects like cracks or slag inclusions, and cansignificantly lower the amount of bismuth used and effectively lower theproduction costs of the low lead brass alloy, such that it is extremelyadvantageous in commercial-scale productions and applications.

Furthermore, the use of the process of the present invention canincrease the yields of lead-free brass products.

The invention has been described using exemplary preferred embodiments.However, it is to be understood that the scope of the invention is notlimited to the disclosed arrangements. The scope of the claims,therefore, should be accorded the broadest interpretation, so as toencompass all such modifications and similar arrangements.

1. A low lead brass alloy, comprising: 0.05 to 0.3 wt % of lead; 0.3 to0.8 wt % of aluminum; 0.01 to 0.4 wt % of bismuth; 0.1 to 0.15 wt % ofmicroelements; and more than 97.5 wt % of copper and zinc, wherein thecopper is in an amount ranging from 58 to 70 wt %.
 2. The low lead brassalloy of claim 1, wherein the lead is in an amount ranging from 0.15 to0.25 wt %.
 3. The low lead brass alloy of claim 1, wherein the aluminumis in an amount ranging from 0.5 to 0.65 wt %.
 4. The low lead brassalloy of claim 1, wherein the bismuth is in an amount ranging from 0.1to 0.2 wt %.
 5. The low lead brass alloy of claim 1, wherein the copperis in an amount ranging from 62 to 65 wt %.
 6. The low lead brass alloyof claim 1, further comprising less than 0.8 wt % of phosphorus.
 7. Thelow lead brass alloy of claim 6, wherein the phosphorus is in an amountranging from 0.4 to 0.8 wt %.
 8. The low lead brass alloy of claim 1,wherein the microelements are at least ones of rare earth elements andunavoidable impurities.
 9. A method for producing a product comprisingthe low lead brass alloy of claim 1, comprising the steps of: preheatingthe low lead brass alloy and foundry return to a temperature rangingfrom 400° C. to 500° C.; melting the low lead brass alloy and thefoundry return to boiling to form a molten copper liquid; preheating amold to 200° C. and placing sand core into the mold; casting the moltencopper liquid into the mold at a temperature ranging from 1010 to 1060°C. to obtain a casting part; and releasing the casting part from themold.
 10. The method of claim 9, further comprising a step of preparingthe sand core by mixing one or more selected from the group consistingof rounded sand having particle diameters respectively ranging from 40to 70 meshes, 50 to 100 meshes and 70 to 140 meshes with a resin and acuring agent.
 11. The method of claim 9, further comprising a step ofperforming a sand washing treatment on the foundry return prior topreheating, so as to remove sand and iron wires.
 12. The method of claim9, wherein the low lead brass alloy and the foundry return are at aweight ratio ranging from 6:1 to 9:1.
 13. The method of claim 9, whereinstep of melting further comprises adding refining slag.
 14. The methodof claim 13, wherein the refining slag is preheated to a temperatureabove 400° C. prior to adding the refining slag.
 15. The method of claim13, wherein the refining slag is added in an amount ranging from 0.10 to0.15 wt % based on a total weight of the low lead brass alloy and thefoundry return.
 16. The method of claim 9, wherein the step of castingis performed for 3 to 8 seconds.
 17. The method of claim 9, wherein thestep of casting is performed in batches, and a casting amount in each ofthe batches is about 1 to 2 kilograms.
 18. The method of claim 9,wherein the step of releasing is performed for 10 to 15 seconds afterstep (d) is completed or till the casting part is not red and hot. 19.The method of claim 9, further comprising: after the step of releasing,cooling the mold and maintaining the mold at a temperature ranging from180 to 220° C.
 20. The method of claim 19, wherein the step of coolingis performed using a graphite liquid.
 21. The method of claim 20,wherein the mold is immersed in the graphite liquid for 3 to 8 seconds.22. The method of claim 20, wherein a specific weight of the graphiteliquid ranges from 1.02 to 1.10.
 23. The method of claim 20, wherein thegraphite liquid is at a temperature ranging from 25 to 45° C.
 24. Themethod of claim 9, further comprising: after the step of releasing,cleaning the mold and spraying the graphite liquid on a surface of themold.